In a Frequency Division Duplexing (FDD) wireless communications system, different frequencies are separately used in uplink transmission and downlink transmission. In a conventional voice communications service, volumes of data that needs to be transmitted in uplink and downlink services are basically the same, and therefore quantities of uplink and downlink transmission resources allocated in the FDD system are the same.
However, with rapid growth of wireless broadband services, multiple service types such as online video and network download are introduced into wireless communications, and a feature of these services is that a data volume of a downlink service is far greater than a data volume of an uplink service. This results in a situation in which there are a lot of idle uplink frequency resources while downlink frequency resources are in shortage on a network. Therefore, currently a dynamic spectrum sharing (DSS) technology is put forward. The DSS technology allows a base station to send a downlink signal on an uplink frequency resource, thereby resolving the problem in the FDD system that uplink frequency resources are idle while downlink frequency resources are in shortage.
In a wireless communications system, out of purposes such as saving energy and avoiding inter-base station interference, maximum transmit powers of base stations are generally limited. For example, in a Long Term Evolution (LTE) system, a maximum transmit power of a macro base station is 46 dbm, and a maximum transmit power of a low-power node (for example, a relay station, a pico base station, or a home base station) is 30 dbm or 24 dbm. However, in the current FDD system, a maximum transmit power of a base station is specified according to only downlink frequency resources. When the DSS technology is used, a base station can send downlink signals on all downlink frequency resources, and sends downlink signals by using some uplink frequency resources. If the base station not only sends a downlink signal but also sends an uplink signal in a same subframe, how the base station coordinates powers for sending the downlink signal on the uplink frequency resource and the downlink frequency resource is not considered.
Therefore, when the DSS technology is used, how a base station coordinates powers for sending a downlink signal on an uplink frequency resource and a downlink frequency resource is an urgent problem to be resolved.